The invention relates to a fine-machining tool, a honing wheel in particular, for machining gear workpieces.
A fine-machining tool such as this, which may be internally geared or externally geared, has a plurality of non-defined cutting edges which are made up of individual cutting grains. These cutting grains may be either ceramic-bonded or resin-bonded. Hence reference is made to a cutting grain in ceramic bonding or cutting grain in plastic bonding. Embedding of fragments of ceramically bonded cutting elements in a plastic material is also now state of the art. Fine-machining tools with ceramic bonding are characterized by good cutting performance and stability of shape but are relatively brittle and thus fracture-prone and impact-sensitive.
Fine-machining tools with plastic bonding, on the other hand, have the advantage of greater elasticity over such tools with ceramic bonding, for which reason they are not as fracture-prone and impact-sensitive. In contrast to this advantage, the cutting performance of such tools is much lower.
The invention is based on the problem of creating a fine-machining tool, a honing wheel in particular, which exhibits adequate elasticity despite high cutting performance.
It is claimed for the invention that a fine-machining tool meeting this requirement, a honing wheel in particular, characterized by an axial laminar structure with a center layer and two exterior layers bonded to each other, the center layer consisting of a plastic material in which cutting grains are embedded, and that the outer layers engaged with the two edge areas of the workpiece consist of ceramically bonded cutting grains.
As a result of the laminar structure of the fine-machining tool claimed for the invention, the advantageous properties of the ceramic bonding, that is cutting force, cutting performance, and guiding function, are not only combined but also reinforce each other. The invention makes use of the finding that the required removal of material is significantly more extensive in the edge area of the gear to be machined than in the center area of the latter, as is explained in detail below. For this reason the layers of higher cutting performance are mounted in the external areas of the fine-machining tool claimed for the invention, while the layer of lower cutting performance but of higher elasticity and better guiding function is mounted in the center area. Experiments have shown that a honing wheel with a structure as claimed for the invention has a tool life several times longer than that of a honing wheel with pure plastic bonding. The fine-machining tool claimed for the invention is especially well suited for machining of workpieces with extensive premachining variations and aggressive flank surfaces. It is also to be used for removal of large amounts of material and for workpieces with burred tooth flanks. The tool claimed for the invention also yields good results if machining of a workpiece must be carried out with a relatively small axis intersection angle. The cutting conditions are more difficult for these workpieces and are improved by use of the ceramic material.
The stable edge areas of the tool characterized by high nondeformability are also of particular advantage in machining of workpieces having an irregular outline (for example, a so-called shoulderwork). Because of this irregular outline, the tool may project only a slight distance above the workpiece, so that the danger exists that the tool will be deformed in this edge area when subjected to the contact pressure.
The thickness of the center layer is approximately 20 to 90 percent of the total thickness of the fine-machining tool claimed for the invention.
The two outer layers are preferably bonded to the center layer by adhesion.
Fragments of ceramically bonded cutting elements may additionally be embedded in the center layer to increase the cutting performance.
An embodiment of the invention is shown in the drawings and discussed in detail below.